Metastasis of Renal Clear Cell Carcinoma to Thyroid Gland Mimicking Adenomatous Goiter

Background: Renal cell carcinoma is an interesting tumor due to its unpredictable behavior. Common metastatic sites of renal cell carcinoma are the lungs, lymph nodes, bones and liver. Concurrent thyroid metastasis of clear cell carcinoma is uncommon but it can appear as a rapidly growing cervical, painless nodular mass. Case Report: We report a case of a 56-year-old male patient with clear cell renal carcinoma confirmed on a histopathological examination. The patient noticed a rapidly growing mass in the thyroid region when receiving medical anticancer therapy. Because of that, gray-scale thyroid ultrasonography and a fine-needle aspiration biopsy were performed. The histopathological examination of the biopsy specimen revealed a lesion composed of malignant epithelial cells compatible with metastasis of renal carcinoma. Conclusions: In patients with with a history of RCC, both past and present, a thyroid mass, especially co-existing with an adenomatous goiter, should prompt a work-up for thyroid metastasis.